Problem: Simplify the following expression: $k = \dfrac{7}{4q} - \dfrac{6}{5q}$
Answer: In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $4q$ and $5q$ $\lcm(4q, 5q) = 20q$ $ k = \dfrac{5}{5} \cdot \dfrac{7}{4q} - \dfrac{4}{4} \cdot \dfrac{6}{5q} $ $k = \dfrac{35}{20q} - \dfrac{24}{20q}$ $k = \dfrac{35 -24}{20q}$ $k = \dfrac{11}{20q}$